Nickel-based catalyst systems are commonly used in the polymerization of 1,3-butadiene monomer into cis-1,4-polybutadiene rubber. Such nickel-based catalyst systems contain (a) an organonickel compound, (b) an organoaluminum compound and (c) a fluorine containing compound. Such nickel-based catalyst systems and their use in the synthesis of cis-1,4-polybutadiene is described in detail in U.S. Pat. No. 3,856,764, U.S. Pat. No. 3,910,869 and U.S. Pat. No. 3,962,375.
The cis-1,4-polybutadiene prepared utilizing such nickel-based catalyst systems typically has a high molecular weight. Due to this high molecular weight, the cis-1,4-polybutadiene is generally oil-extended. However, this precludes the cis-1,4-polybutadiene from being utilized in many applications. For instance, such oil-extended rubbers cannot be utilized in tire sidewalls which contain white sidewall compounds. In any case, there is a large demand for cis-1,4-polybutadiene having a reduced molecular weight which can be processed without being oil-extended.
Various compounds have been found to act as molecular weight-reducing agents when used in conjunction with the nickel-based catalyst system. For instance, U.S. Pat. No. 4,383,097 discloses that alpha-olefins, such as ethylene and propylene, act as molecular weight-reducing agents when utilized in conjunction with such three-component nickel catalyst systems. U.S. Pat. No. 5,698,643 indicates that 1-butene, isobutylene, cis-2-butene, trans-2-butene and allene act as molecular weight regulators when used in conjunction with such nickel-based catalyst systems. U.S. Pat. No. 4,383,097 reveals that certain nonconjugated diolefins, such as 1,4-pentadiene, 1,6-heptadiene and 1,5-hexadiene, act as molecular weight-reducing agents when utilized in conjunction with such catalyst systems. U.S. Pat. No. 5,100,982 indicates that cis-1,4-polybutadiene having reduced molecular weight and a broad molecular weight distribution can be synthesized with certain nickel-based catalyst systems in the presence of halogenated phenols, such as para-chlorophenol.
The processability of cis-1,4-polybutadiene rubbers can be improved by simply lowering their molecular weight. However, this approach also typically leads to increased cold flow. Accordingly, the use of conventional molecular weight-reducing agents, such as xcex1-olefins, to improve rubber processability leads to compromised cold flow characteristics.
U.S. Pat. No. 5,451,646 discloses that para-styrenated diphenylamine acts as a molecular weight-reducing agent when employed in conjunction with nickel-based catalyst systems which contain (a) an organonickel compound, (b) an organoaluminum compound and (c) a fluorine containing compound. The teachings of U.S. Pat. No. 5,451,646 also indicate that para-styrenated diphenylamine acts to improve the processability of cis-1,4-polybutadiene rubbers prepared in their presence utilizing such nickel-based catalyst systems. Para-styrenated diphenylamine can be employed in conjunction with such nickel-based catalyst systems to reduce the molecular weight of the rubber without sacrificing cold flow characteristics. The para-styrenated diphenylamine which remains in the rubber produced also acts in a manner which provides it with antioxidant protection. In other words, the para-styrenated diphenylamine accomplishes two major objectives. It acts as a molecular weight regulator and acts as an antidegradant.
U.S. Pat. No. 5,451,646 specifically discloses a process for producing cis-1,4-polybutadiene having a reduced molecular weight and improved processability which comprises polymerizing 1,3-butadiene in the presence of (a) an organonickel compound, (b) an organoaluminum compound, (c) a fluorine containing compound and (d) para-styrenated diphenylamine; wherein the organoaluminum compound and the fluorine containing compound are brought together in the presence of the para-styrenated diphenylamine.
U.S. Pat. No. 4,929,678 discloses a rubber composition for a solid golf ball having excellent durability and rebound properties comprising: (a) a rubber component comprising at least 40 percent by weight of a polybutadiene rubber which has a Mooney ML 1+4 viscosity of 50 to 70 and a cis-1,4 bond content of at least 80 percent, (b) a co-crosslinking agent and (c) a peroxide.
It has been found that blends of cis-1,4-polybutadiene rubber with other rubbery polymers offer improved processability and improved physical characteristics in cases where the cis-1,4- polybutadiene rubber is synthesized by polymerizing 1,3-butadiene in the presence of (a) an organonickel compound, (b) an organoaluminum compound, (c) a fluorine containing compound and (d) para-styrenated diphenylamine. Such cis-1,4-polybutadiene rubber blends offer improved processability and enhanced physical properties. For instance, improved mixing which results in better incorporation of pigments and fillers, such as carbon black and silica, at lower levels of power consumption is realized. Additionally, improvements in tear resistance with little sacrifice in hysteretic properties, abrasion resistance and modulus are also attained with the rubber blends of this invention. The rubber blends of this invention can be used in manufacturing a wide variety of rubber products, such as tires, hoses, belts, golf balls, tennis balls, racquet balls, golf club grips, stoppers, plungers, tubing, straps, diaphragms, motor mounts, bushings, weather stripping, windshield wiper blades, shoe soles, other molded rubber products and adhesives.
The present invention more specifically discloses a golf ball which is comprised of a solid core and a resin cover, wherein the solid core is comprised of cis-1,4-polybutadiene rubber which is made by polymerizing 1,3-butadiene in the presence of (a) an organonickel compound, (b) an organoaluminum compound, (c) a fluorine containing compound and (d) para-styrenated diphenylamine; wherein the organoaluminum compound and the fluorine containing compound are brought together in the presence of the para-styrenated diphenylamine.
The present invention further reveals a rubber composition for a solid golf ball having excellent durability and rebound properties comprising: (a) cis-1,4-polybutadiene rubber, wherein said cis-1,4-polybutadiene rubber has a Mooney ML 1+4 viscosity of 35 to 70, wherein said cis-1,4-polybutadiene rubber has a cis-1,4 bond content of at least 95 percent, wherein cis-1,4-polybutadiene rubber is made by polymerizing 1,3-butadiene in the presence of (a) an organonickel compound, (b) an organoaluminum compound, (c) a fluorine containing compound and (d) para-styrenated diphenylamine, and wherein the organoaluminum compound and the fluorine containing compound are brought together in the presence of the para-styrenated diphenylamine; (b) a co-crosslinking agent and (c) a peroxide.
The present invention also discloses a tire tread compound which is comprised of (1) about 40 phr to about 60 phr of cis-1,4-polybutadiene, wherein cis-1,4-polybutadiene rubber is made by polymerizing 1,3-butadiene in the presence of (a) an organonickel compound, (b) an organoaluminum compound, (c) a fluorine containing compound and (d) para-styrenated diphenylamine, wherein the organoaluminum compound and the fluorine containing compound are brought together in the presence of the para-styrenated diphenylamine; and (2) about 40 phr to about 60 phr of at least one rubbery polymer selected from the group consisting of natural rubber, solution styrene-butadiene rubber and emulsion styrene-butadiene rubber.